1. Field of the Invention
The present invention generally relates to mobile communication systems.
In a general way, mobile communication systems are subject to standardisation; therefore details on such systems can be found in the corresponding standards, published by the corresponding standardisation bodies.
2. Description of the Prior Art
It is simply recalled that such systems, such as for example 3GPP (2G-3G) systems, comprise:                Mobile Stations (MS), also called User Equipments (UE)        a Radio Access Network (RAN), in turn comprising Base Stations (BS) also called Node B, and Base Station Controllers (BSC) also called Radio Network Controllers (RNC),        a Core Network (CN), in turn comprising entities such as in particular Mobile Switching Center (MSC) for a Circuit Switched (CS) domain, and Serving GPRS Support Nodes (SGSN) for a Packet-Switched (PS) domain.        
It is recalled that in such systems, establishing a connection with a mobile station requires establishing a signalling (or control plane) connection, and a user plane connection.
It is also recalled that, from a Mobility Management (MM) point of view, for the CN PS domain, a mobile station moves from a so-called idle mode to a so-called connected mode when a signalling connection is established for this mobile station, or moves back from the connected mode to the idle mode when the signalling connection is released due e.g. to inactivity of the mobile station.
It is also recalled that in idle mode the CN only keeps track of the mobile station within the accuracy of a set of cells, also called Location Area (LA), or Routing Area (RA) in the case of the PS domain, and a paging procedure is required before establishing a connection with a mobile station in idle mode.
In the case of a packet connection, the signalling connection may be released by the network when there is not enough activity on the user plane connection. If there is again some activity, a problem is the delay introduced by the re-establishment of a connection, which is a relatively long process, requiring a relatively high number of steps, according to usual procedures, as now recalled in relation with FIG. 1.
At step 1, a network entity in charge of initiating a paging procedure, or paging initiator (e.g. SGSN) sends a paging request to network entities, or paging distributors (e.g. RNC or BSC/PCU (Packet Control Unit)), in charge of forwarding the paging request to all BS/Node B of the Location Area (LA) or Routing Area (RA) where the MS/UE has previously been localized.
At step 2, each paging distributor forwards the paging request to all BS/Node B of the Location Area (LA) or Routing Area (RA) where the MS/UE has previously been localized.
At step 3, paging messages are sent from each BS/Node B of the LA/RA over the radio interface. These messages contain the identity of the MS/UE to be paged.
At step 4, a paging response is sent by the MS/UE to a BS/Node B, or serving BS/Node B. The UE answers to the paging request, with the value of UE/MS's identity used in the paging message.
At step 5, a signalling connection, or RRC (Radio Resource Control) connection is established between the MS/UE and the serving BS/Node B.
At step 6, the paging response of the MS/UE is forwarded by the serving BS/Node B to the paging distributor, and further on by this paging distributor to the paging initiator.
At step 7, a security mode command is sent by the paging initiator (e.g. SGSN) to the serving BS/Node B, to establish mobility and security (MM) contexts of the MS/UE (this security mode command carrying parameters such as ciphering and integrity keys, and allowed algorithms).
At step 8, the serving BS/Node B commands the MS/UE to apply the security parameters received from the paging initiator (e.g. SGSN) and security algorithms are negotiated. Though not specifically illustrated in FIG. 1, step 8 comprises a first step wherein the serving BS/Node B sends a security mode command to the MS/UE, and a second step wherein the MS/UE sends a security mode response to the serving BS/Node B.
At step 9, a security mode complete is sent in response from the serving BS/Node B to the paging initiator (SGSN).
At step 10, a RAB (Radio Access Bearer) assignment request is sent from the paging initiator (SGSN) to the serving BS/Node B (this assignment request containing such parameters as parameters describing the QoS properties of the bearers to be established for the MS/UE).
At step 11, a RB (Radio Bearer), for user plane connection, is established between the serving BS/Node B and the MS/UE. Though not specifically illustrated in FIG. 1, step 11 comprises a first step wherein the serving BS/Node B sends a Radio Bearer setup request to the MS/UE, and a second step wherein the MS/UE sends a Radio Bearer setup complete to the serving BS/Node B.
At step 12, a RAB assignment response is sent from the serving BS/Node B to the paging initiator (SGSN).
At step 13, the MS/UE can actually receive the data.
FIG. 2 is intended to illustrate an example of calculation of the setup delays with a method according to the prior art as recalled in FIG. 1.
The assumptions for delay calculation in this example are as follows:
Transmission time:                between CN and BS/ENB (due to microwave transport): 5 ms        from BS/ENB to BS/ENB (due to 2 hops of microwave): 8 ms        air interface (assuming RRC messages can be transmitted in 1 TTI (Transmission Time Interval)): 0.5 ms        
Processsing time:                UE internal processing time for RRC messages: 10 ms        ENB internal time for signalling messages: 10 ms (assumed to be the same as RRC processing time in UE/MS)        Paging initiator (CN) internal processing time for signalling messages: 10 ms (assumed to be the same as RRC processing time in UE/MS)        
In this example, it can be seen that the total delay at the MS/UE is 165 ms.